This invention relates to a fluid absorber for a suction tube set. More particularly, this invention relates to a fluid absorber for a suction tube set for use in laser eye surgery.
As is known, various types of devices and equipment have been utilized in surgical procedures performed on an eyeball and particularly for photoretractive keratectomy laser surgery. During such procedures, a weak laser beam is used to remove tiny layers of tissue and to reshape the cornea to improve sight. Typically, photoretractive keratectomy is accomplished by an excimer laser beam that ablates away corneal tissue in a photodecomposition process. Before this occurs, a flap of the epithelium of the cornea is surgically removed to expose Bowman""s layer on the anterior surface of the stroma. The excimer laser beam is then used for laser ablation at Bowman""s layer. The laser beam is also used to remove corneal tissue to varying depths as necessary for re-contouring the anterior stroma. Afterward, the epithelium flap is repositioned to rapidly regrow and resurface the contoured area.
In order to stabilize an eyeball for purposes of such a surgical laser operation, it has been known to fix the eyeball in place using a suction device. This allows a surgeon to operate on the eyeball without the risk that the eyeball may move during the operation.
One known device for stabilizing an eyeball and for effecting removal of an epithelium flap is an automated disposable keratome sold by LaserSight Technologies, Inc. of Winter Park, Fla. This instrument provides a ring which is to be placed on the eyeball as well as a keratome for slicing a flap in the epithelium of the eyeball. Once the ring is in place with suction on, the keratome can be operated by a surgeon to cut the flap. High suction is generally required briefly to raise the LOP (intraocular pressure) and keep the eye rigid so that a clean cut can be made. However, there is a danger involved with such instruments if there is a loss of suction during this cutting time. Accordingly, the instrument is provided with an alarm that warns a surgeon instantly if suction is lost.
Studies have shown that the IOP rises to over 99 mmHg at maximum suction, with the estimated actual IOP during maximum suction being as high as 130 or 140 mmHg. However, prolonged exposure to this level of IOP creates a potential for damage to delicate retinal structures. Thus, in order to preclude damage, the time of exposure to high vacuum is limited to an absolute minimum.
Thus, with the suction ring in place and the vacuum set at 5 inches of mercury (Hg), the patient""s IOP rises to the 30-35 mmHg range. This relatively safe level of vacuum is enough to hold the ring in place but not enough to produce a good cut. So when the surgeon activates the keratome, the vacuum rises immediately to 24 inches of mercury, pushing the IOP high enough for a good cut. However, the high vacuum lasts only for the 2 to 3 seconds required for the keratome to go forward across the ring. When the keratome goes back, the vacuum drops down again to 5 inches Hg, enough to hold the ring in place but not enough to endanger the retina and optic nerve.
Another problem which arises during an eye operation of the above type is due to the fact that tearing of the eyeball usually occurs so that fluid, i.e. salt water, is drawn into the suction ring and eventually into the vacuum pump. Should fluid begin to enter the vacuum pump, the pump can cease to draw a vacuum so that the eyeball is no longer locked in place. This is particularly the case where the pump retains fluid from a succession of eye operations.
In order to prevent fluids from migrating into the vacuum pump, fluid traps have been incorporated in the suction line between the vacuum pump and eyeball-engaging ring. That is to say, the line from the ring terminates in a vertically disposed trap to deliver fluid into the trap while a second line extends from the trap to the vacuum pump in order to conduct a vacuum force from the vacuum pump. Typically, the two lines are sealed relative to the interior of the trap so that a xe2x80x9creservoirxe2x80x9d of fluid can be accumulated within the trap while an air space is provided above the xe2x80x9creservoirxe2x80x9d of fluid to conduct an air flow therethrough. One of the problems with such a trap is that the trap must be maintained vertical as the trap operates under gravity. Accordingly, care must be taken to ensure that the trap does not turn upside down, as otherwise, fluid would immediately pass into the vacuum pump thereby rendering the pump inoperative.
It has also been known to place filters in the suction tube lines in order to prevent fluid coming from an eyeball to pass onto the vacuum pump. However, one problem associated with this technique is that as the eyeball side of the filter become filled with fluid, the resistance in the line to air flow increases. Thus, instead of the vacuum rising to 24 inches of mercury at the eyeball, a smaller vacuum force is generated at the ring-eyeball interface with the risk that a good cut in the epithelium may become compromised.
Another problem which may arise during an operation is that which is associated with a slight movement of the ring from the eyeball through accident or inadvertence which may cause a slight break in the vacuum due to a separation between the ring and the eyeball. Should this occur, an alarm would be sounded or visually indicated to the surgeon so that the ring may be reoriented and re-attached to the eyeball. However, if a filter has been provided in the suction line which has become filled with fluid on the eyeball side, the recovery time for the reengaging the ring with the eyeball is prolonged. In such a case, an eyeball movement can occur.
Accordingly, it is an object of the invention to reduce the risk of interrupting a photoretractive keratectomy laser operation due to a loss of vacuum caused by an accumulation of fluid in a vacuum pump.
It is another object of the invention to preclude an accumulation of fluid in a vacuum pump for instruments used in photoretractive keratectomy laser surgery.
It is another object of the invention to be able to trap fluid in a suction line set for a keratome without significantly increasing the resistance to air flow in the suction line.
Briefly, the invention provides a fluid absorber for a suction tube set for a keratome wherein the fluid absorber comprises a hollow housing for connection at one side to a vacuum pump and for connection at an opposite side to the keratome and a formed absorbent mass in the housing for absorbing fluid emanating from an eyeball without increasing the resistance to air flow at saturation by more than 3 inches of mercury. Typically, the absorbent mass is a cellulosic sponge mass.
In addition, the housing has a cap at each end with a spigot to receive either a suction tube or an inlet tube as the case may be. In addition, the fluid absorber includes a pair of spacer tubes, each of which is located between the sponge mass and the respective cap. These spacer tubes serve to space the sponge mass away from the spigot openings in the end caps in order to avoid clogging of the spigots. In addition, the spacer tubes serve to compress the sponge mass therebetween. This compression not only expands the sponge mass radially to engage against the inner diameter of the housing and close any space therebetween but also eliminates any through passage through the cells of the sponge mass from one end to the other.
In another embodiment, the sponge mass may be fixedly secured to the housing, for example by means of an adhesive at each end thereof, in order to prevent sliding of the sponge mass within the housing under a suction force of the vacuum pump.
The invention also provides a suction tube set which is comprised of the fluid absorber, a suction tube connected to one end of the housing of the fluid absorber for drawing a vacuum force within the housing and an inlet tube connected to and extending from an opposite end of the housing of the fluid absorber for conveying a vacuum force therethrough.
The suction tube set is connected to and between an eyepiece for fitting against an eyeball and a vacuum pump for drawing a vacuum at the eyepiece-eyeball junction. For example, the eyepiece may be the ring of an automated disposable keratome as sold by LaserSight Technologies Inc. of Winter Park, Fla. This ring is sized to engage an eyeball and has a plurality of ports for communicating with a passageway in the inlet tube.
The absorbent mass is particularly characterized in being able to absorb fluid without increasing the resistance to air flow by no more than 2 inches to 5 inches of mercury (Hg). The amount of fluid which is absorbed by the absorbent mass is based upon the expected amount of fluid which would be generated during an operation and by the amount of resistance created by a fluid-filled mass. That is to say, the absorbent mass is characterized in being able to absorb the amount of fluid expected to be generated during an operation without significantly increasing the resistance to air flow through the absorbent mass.
The purpose of forming a gap between the caps of the housing and the sponge mass is to avoid the sponge covering over the apertures of the respective caps which communicate with the suction line, as otherwise, the resistance to air flow could increase significantly thereby giving a false high value at the vacuum pump to a surgeon that the eyeball to which the eyepiece is locked may have become released and may have moved. In addition, a significant increase in air flow resistance would significantly increase the response time should vacuum be lost at the eyeball-eyepiece junction. This would also negate a safety pressure differential system at the vacuum pump which would notify the surgeon that vacuum has been lost.
Where the absorbent mass is a cellulosic sponge mass, it has been known to manufacture such sponges with an anti-bacterial agent in order to prevent the growth of mold and the like. In accordance with the invention, the cellulosic sponge mass is compressed to squeeze out the antibacterial agent. Further, compression of the sponge mass reduces the chance that there may be a continuous passage through the sponge mass for a flow of fluid. Typically, the sponge mass can be gamma sterilized to achieve a sterile product.
Further, it has been found that compression of the cellulosic sponge mass has little effect on the air flow resistance through the sponge mass.
Typically, the cellulosic sponge mass is hydrophillic and is commercially available under the trademark OCELLO and is sold by the 3M Company. Other types of sponge material may be polyurethane, hydrophillic polyethylene and polypropylene.